a) Demonstrate understanding of the covalent bond in terms of electron sharing b) Interpret and construct ‘dot and cross’ diagrams of simple covalent compounds c) Demonstrate understanding of the terms bond length and bond angle d) Predict and interpret the shapes and bond angles in simple molecules and ions using electron-

pair repulsion theory (up to four outer pairs of electrons present as bonding pairs and lone pairs)

Molecules vary in shape as shown by the following examples: ElectronElectronElectronElectron----pair repulsion theorypair repulsion theorypair repulsion theorypair repulsion theory

• Electrons are negatively charged so they repel each other. • They can pair up with opposite spins in orbitals and the same is also true in molecules. • Electron pairs in the outer most bonding shell will repel other electron pairs in the same shell. • The effect is that these pairs will try and move as far apart from one another as possible within the confines of the molecule.

This theory determines the 3D shape of the molecule. Counting the electron pairs on a molecule allows its shape to be predicted. 4 bonding pairs4 bonding pairs4 bonding pairs4 bonding pairs eg. Methane

• The bonding pairs of electrons are repelled as far away as possible from each other • This forms a regular tetrahedrontetrahedrontetrahedrontetrahedron with 109.5° bond angles. 3 bonding pairs and 1 lone pair3 bonding pairs and 1 lone pair3 bonding pairs and 1 lone pair3 bonding pairs and 1 lone pair eg. Ammonia

• Lone pairs have more repulsion than bonding pairs • So the lone pair pushes the three hydrogens slightly closer together to form a trigonal pyramidaltrigonal pyramidaltrigonal pyramidaltrigonal pyramidal structure.

• Bond angle 107°

2 bonding pairs and 2 lone pairs2 bonding pairs and 2 lone pairs2 bonding pairs and 2 lone pairs2 bonding pairs and 2 lone pairs eg. Water

• Two lone pairs push the two bonding pairs even further together making the two hydrogens even closer

• Bond angle of 104.5° • Non linear Non linear Non linear Non linear (or bent molecule) 4 electron pairs but in two double bonds4 electron pairs but in two double bonds4 electron pairs but in two double bonds4 electron pairs but in two double bonds eg. CO2

• Consider double bonds to behave the same as one single bond • They will repel the other double bond as much as possible and therefore be 180° apart. • Linear moleculeLinear moleculeLinear moleculeLinear molecule 3 bonding pairs3 bonding pairs3 bonding pairs3 bonding pairs eg. BF3

• The 3 pairs will repel each other as far as possible - 120° • Trigonal PlanarTrigonal PlanarTrigonal PlanarTrigonal Planar 6 bonding pairs6 bonding pairs6 bonding pairs6 bonding pairs eg. SF6

• Repulsion between all the pairs leads to bond angles of 90° • OctahedronOctahedronOctahedronOctahedron (with 8 faces)

e) Demonstrate understanding of the terms σ-bond and π-bond, including the electron density in each type

f) Demonstrate understanding of the term electronegativity g) Select data in order to predict the nature of the structure and bonding in a given substance

(simple molecular or giant covalent), including dative covalency, bonding of intermediate type, bond polarity and delocalisation.

h) Demonstrate understanding of the terms: enthalpy change of atomisation, enthalpy change of combustion and bond enthalpy.

i) Calculate bond energies, using Hess’s Law and selecting appropriate data. j) Understand the relationship of bond energies to the activation energy of a reaction and how

molecular collisions contribute to the rate of a reaction (qualitative only) k) Understand that catalysts speed up chemical reactions by providing alternative routes of lower

activation energy l) Understand that increases of temperature speed up chemical reactions by increasing the

proportion of molecules with the necessary activation energy (qualitative only) m) Recall that some reactions are reversible and understand the dynamic nature of equilibrium

reactions; be able to predict the effect of a change in concentration, temperature or pressure on the position of an equilibrium of a reaction (in simple qualitative cases only)

1. (a) Boron, nitrogen and oxygen form fluorides with molecular formulae BF3, NF3 and OF2.

Draw the shapes you would expect for these molecules, suggesting a value for the bond angle in each case.

BF3

FBF bond angle =

NF3

FNF bond angle =

OF2

FOF bond angle = (3)

(b) (i) Calculate the standard enthalpy change of atomization of nitrogen trifluoride, ∆H e[NF3(g)]. Your answer should include a sign and units.

Use the Hess cycle, and the data at 298 K:

∆H f [NF3(g)] = –124.7 kJ mol–1

∆H e [½N2(g)] = +472.7 kJ mol–1

∆H e [½F2(g)] = +79.0 kJ mol–1

NF (g) N(g) + 3F(g)∆H [NF (g)]

∅

at 33

∆H [NF (g)]∅

3f12

32N (g) + F (g)22

(3)

(ii) Use your answer to (i) to calculate the bond energy of the N–F bond (1)

(c) Another fluoride of nitrogen has the formula N2F2.

(i) Draw a ‘dot–and–cross’ diagram for the electronic structure of N2F2 showing outer shell electrons only.

(2)

(ii) Draw diagrams to show two possible shapes for the N2F2 molecule

(1)

(iii) The N–F bond energy in N2F2 is 282.0 kJ mol–1. Suggest a reason for the differences between this value and the value you calculated for the N–F bond in NF3 in (b)(ii).

..........................................................................................................................

.......................................................................................................................... (1)

(d) BF3 and NF3 react together readily to give a solid with composition BN3NF3.

(i) Draw a ‘dot–and ‘cross’ diagram for the electronic structure of BF3NF3 showing outer shell electrons only.

(1)

(ii) What is the type of bond between the nitrogen and boron atoms?

.......................................................................................................................... (1)

(e) Suggest a balanced equation for the reaction of 1 mole of OF2 with 1 mole of water to form two products.

(2)

(Total 15 marks)

2. (a) Boron, nitrogen and oxygen form fluorides with molecular formulae BF3, NF3 and OF2.

Draw the shapes you would expect for these molecules, suggesting a value for the bond angle in each case.

BF3

FBF bond angle =

NF3

FNF bond angle =

OF2

FOF bond angle = (3)

(b) (i) Calculate the standard enthalpy change of atomization of nitrogen trifluoride, ∆H e [NF3(g)]. Your answer should include a sign and units.

Use the Hess cycle, and the data at 298 K:

∆H f [NF3(g)] = –124.7 kJ mol–1

∆H e[½N2(g)] = +472.7 kJ mol–1

∆H e[½F2(g)] = +79.0 kJ mol–1

NF (g) N(g) + 3F(g)∆H [NF (g)]

∅

at 33

∆H [NF (g)]∅

3f12

32N (g) + F (g)22

(3)

(ii) Use your answer to (i) to calculate the bond energy of the N–F bond. (1)

(c) Another fluoride of nitrogen has the formula N2F2.

(i) Draw a ‘dot–and–cross’ diagram for the electronic structure of N2F2 showing outer shell electrons only.

(2)

(ii) Draw diagrams to show two possible shapes for the N2F2 molecule.

(1)

(iii) The N–F bond energy in N2F2 is 282.0 kJ mol–1. Suggest a reason for the difference between this value and the value you calculated for the N–F bond in NF3 in (b)(ii).

..........................................................................................................................

.......................................................................................................................... (1)

(d) BF3 and NF3 react together readily to give a solid with composition BN3NF3.

(i) Draw a ‘dot-and ‘cross’ diagram for the electronic structure of BF3NF3 showing outer shell electrons only.

(1)

(ii) What is the type of bond between the nitrogen and boron atoms?

.......................................................................................................................... (1)

(e) Suggest a balanced equation for the reaction of 1 mole of OF2 with 1 mole of water to form two products.

(2)

(Total 15 marks)

3. Cynogen, (CN)2, behaves like the halogens in its chemical reactions. Its hydride, hydrogen cyanide, HCN, is similar to the hydrogen halides.

(i) Draw ‘dot–and–cross’ diagrams of hydrogen chloride, hydrogen cyanide and cyanogen molecules. You need include only outer shell electrons.

hydrogen chloride

hydrogen cyanide

cyanogen

(3)

(ii) Draw the displayed formula for cyanogen showing the CCN bond angle.

(2)

(Total 5 marks)

4. Electron density maps for sodium chloride, a hydrogen molecule ion, +2H , and a benzene molecule are

shown below.

(a) (i) Describe fully the difference between the contours of the electron density maps for

sodium chloride and the hydrogen molecule ion, +2H .

….………………………………………………..……………………………

….………………………………………………..……………………………

….………………………………………………..……………………………

….………………………………………………..…………………………… (2)

(ii) What does the difference in (i) tell you about the distribution of electrons in molecules

compared with ionic compounds?

….………………………………………………..……………………………

….………………………………………………..……………………………

….………………………………………………..……………………………

….………………………………………………..…………………………… (2)

(iii) Draw a `dot–and–cross' diagram for a hydrogen molecule ion, +2H .

(1)

(b) (i) What is the typical characteristic of some of the bonding electrons in an arene compound like benzene?

….………………………………………………..…………………………… (1)

(ii) How does the electron density map for benzene demonstrate this characteristic?

….………………………………………………..…………………………… (1)

(Total 7 marks)

5. (a) (i) The gas hydrogen iodide decomposes when heated to form hydrogen and iodine.

Describe how you would carry out this reaction in the laboratory, if you were provided with a test tube of hydrogen iodide.

............................................................................................................................

............................................................................................................................ (1)

(ii) What would you expect to see as the reaction takes place?

............................................................................................................................ (1)

(b) A mixture of hydrogen iodide, hydrogen and iodine (all in the gaseous state) establishes dynamic equilibrium if a constant temperature is maintained.

2HI (g) H2 (g) + I2 (g) ∆H = +9.6 kJ mol–1

(i) Explain the meaning of the term dynamic equilibrium.

............................................................................................................................

............................................................................................................................

............................................................................................................................ (2)

(ii) How, if at all, would the proportion of hydrogen iodide present at equilibrium change if the temperature were to be increased? Justify your answer.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................ (2)

(iii) The reaction is catalysed by metals such as gold and platinum. How, if at all, would the proportion of hydrogen iodide present at equilibrium change if the reaction were to be catalysed? Justify your answer.

............................................................................................................................

............................................................................................................................ (1)

(c) Part of an energy profile for this reaction is shown below. It is not intended to be to scale.

Complete the profile showing:

• the products;

• the progress of both uncatalysed and catalysed reactions;

• labelled arrows to indicate the activation energies of both the uncatalysed and catalysed reactions.

(4) (Total 11 marks)

6. This question is concerned with hydrogen cyanide, HCN.

(a) (i) Draw a ‘dot and cross’ diagram for a molecule of hydrogen cyanide, showing outer shell electrons only.

(1)

(ii) Predict the numerical value of the bond angle in hydrogen cyanide. Justify your prediction.

Bond angle ........................................................................................................

Justification .......................................................................................................

..........................................................................................................................

.......................................................................................................................... (2)

(b) Write a balanced equation for the combustion of hydrogen cyanide in oxygen, assuming that the products are water, carbon dioxide and nitrogen.

(1)

(c) Hydrogen cyanide is an extremely toxic, volatile liquid that is used to make useful compounds, such as ‘Perspex’. Do you think it is acceptable for it to be used in this way?

Justify your answer.

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (1)

(d) The standard enthalpy change of formation, ∆Hf

ο, for gaseous hydrogen cyanide, HCN(g), is

+110 kJ mol–1.

The standard molar enthalpy changes of atomisation of hydrogen, carbon and nitrogen are given below, in kJ mol–1.

∆Hοat/kJ mol–1

½H2(g) → H(g) + 218 C(s, graphite) → C(g) + 717

21 N2(g) → N(g) + 473

The C–H bond energy in hydrogen cyanide is + 413 kJ mol–1.

This information can be represented on a Hess cycle in the following way, and then used to calculate a bond energy.

(i) Insert formulae, showing the correct quantities of each element, into the appropriate boxes.

(2)

(ii) Insert arrows between the boxes and write the correct numerical data alongside the appropriate arrows.

(2)

(iii) Use the cycle to calculate ∆Hοat[HCN(g)] and then the carbon to nitrogen bond energy in hydrogen cyanide.

(1)

(Total 10 marks)

7. The industrial processes involved in the production of poly(chloroethene) are summarised in the flow chart:

ethane → ethene → 1,2-dichloroethane → chloroethene → poly(chloroethene)

(a) (i) Ethane is converted to ethene by dehydrogenation.

Write a balanced equation, including state symbols, for this equilibrium reaction.

(1)

(ii) Explain why conditions of high pressure are less favourable for ethene production.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................ (2)

(b) Draw a labelled diagram of an ethene molecule, showing the electron density distribution in the σ and π bonds between the carbon atoms.

(2)

(c) Give a chemical test which would distinguish between ethane and ethene.

State the result of your test with ethene.

Test ..............................................................................................................................

Result ........................................................................................................................... (2)

(d) 1,2-dichloroethane is formed from ethene by reaction with chlorine.

State the type and mechanism of this reaction.

Type ...................................................................................................................................

Mechanism ......................................................................................................................... (2)

(e) (i) Suggest a reagent and TWO conditions for making chloroethene from

1,2-dichloroethane in the laboratory.

Reagent .......................................................................................................................

Conditions ................................................................................................................... (2)

(ii) Name both types of intermolecular force between chloroethene molecules.

.............................................................................................................................

............................................................................................................................. (1)

(f) (i) Write a balanced equation for the formation of poly(chloroethene) from chloroethene.

(2)

(ii) Poly(chloroethene) is also known by the name polyvinylchloride, PVC.

Give TWO common uses of poly(chloroethene).

.............................................................................................................................

............................................................................................................................. (2)

(Total 16 marks)

8. Phosphine, PH3, is a hydride of the Group 5 element, phosphorus.

(a) (i) Draw a ‘dot-and-cross’ diagram of a phosphine molecule. You should include only outer shell electrons.

(1)

(ii) Draw the shape you would expect for the phosphine molecule, suggesting a value for the HPH bond angle.

HPH bond angle ....................................................................................................... (2)

(iii) Explain the shape of the phosphine molecule you have given in your answer in (ii).

Justify your value for the HPH bond angle.

.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

............................................................................................................................. (2)

(b) (i) Write a balanced equation, including state symbols, for the atomisation of phosphine gas.

............................................................................................................................. (1)

(ii) Use your answer to (i) and the data below to calculate the standard enthalpy change of atomisation of phosphine at 298 K. Include a sign and units in your answer.

∆Hοf[PH3(g)] = + 5.4 kJ mol−1

∆Hοat[½H2(g)] = + 218.0 kJ mol−1

∆Hοat[P(s)] = + 314.6 kJ mol−1

(3)

(iii) Calculate a value for the bond energy of the bond between phosphorus and hydrogen, using your answer to (ii).

(1)

(Total 10 marks)

9. But-1-ene, CH2==CHCH2CH3, can be converted into a polymer.

(a) Draw the structure of part of the polymer, showing TWO repeating units.

(2)

(b) The polymerisation of CH2==CHCH2CH3 is exothermic and involves the use of a catalyst. The diagram below shows the energy profile for this polymerisation using a catalyst.

Indicate on the profile the activation energy for the catalysed process.

Add another energy profile to the diagram for the polymerisation where a catalyst is not used. (3)

(c) Explain, in terms of activation energy and the collision theory, why the rate of polymerisation is greater when

(i) a catalyst is used

...............................................................................................................................

...............................................................................................................................

............................................................................................................................... (1)

(ii) heat energy is provided to start the process.

...............................................................................................................................

...............................................................................................................................

............................................................................................................................... (1)

(Total 7 marks)

10. This question is about the chemistry of methanol, CH3OH.

(a) (i) Draw a ‘dot and cross’ diagram for methanol, showing outer shell electrons only.

(1)

(ii) Textbooks show the displayed formula of methanol as follows

However, this is not a true representation of the shape of the molecule. Explain why the shape of methanol is not as shown above. Label the correct value of ONE bond angle on the displayed formula.

................................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................ (2)

(b) When methanol burns in a poor supply of air, one of the products is carbon monoxide. A ‘dot and cross’ diagram of carbon monoxide is shown below.

(i) Draw the displayed formula for carbon monoxide. Show the TWO types of bond which are present.

(1)

(ii) The length of the bond between carbon and oxygen in methanol is 0.143 nm. Would you expect the length of the bond between carbon and oxygen in carbon monoxide to be longer, the same or shorter than this? Explain your answer.

................................................................................................................................

................................................................................................................................

................................................................................................................................ (2)

(c) The energy of the bond between carbon and oxygen in methanol (the C—O bond) can be calculated from data on enthalpy changes of atomisation.

(i) Write an equation, including state symbols, for the atomisation of one mole of methanol vapour.

(1)

(ii) Use the data below to calculate the energy of the C—O bond in methanol.

standard enthalpy change of atomisation of methanol vapour, ∆Hοat = +2039 kJ mol–1

energy of C—H bond, E(C—H) = +413 kJ mol–1

energy of O—H bond, E(O—H) = +464 kJ mol–1

(2)

(iii) Complete a balanced Hess cycle which you can use to calculate the standard enthalpy change of formation of methanol vapour, ∆Hοf.

You should use the value of the standard enthalpy change of atomisation of methanol vapour, ∆Hοat, given in (ii) and the data on enthalpy changes given below. Write the correct numerical data beside the arrows in the cycle.

Equation Enthalpy change of atomization /kJ mol–1

C(graphite) → C(g) +716.7 ½ O2(g) → O(g) +249.2 ½ H2(g) → H(g) +218.0

Use your cycle to calculate the value of ∆Hοf for methanol vapour.

(3)

(iv) Methanol is a liquid at room temperature. Would you expect the standard enthalpy change of formation of liquid methanol to be more or less negative than the value you calculated in (iii)? Justify your answer.

................................................................................................................................

................................................................................................................................ (1)

(v) Methanol is a liquid at room temperature although alkanes with similar molecular mass are gases.

Draw a diagram to show a bond between two methanol molecules that causes it to be a liquid at room temperature.

Give the value of this bond angle on your diagram.

(2)

(d) Methanol can be manufactured in the following reaction.

CO(g) + 2H2(g) CH3OH(g) ∆Hο = –93.3 kJ mol–1

Decide whether a high or low temperature and a high or low pressure would give the greater proportion of methanol at equilibrium. Justify your choice in each case.

Temperature ..................................................................................................................

.......................................................................................................................................

.......................................................................................................................................

Pressure .........................................................................................................................

.......................................................................................................................................

....................................................................................................................................... (2)

(Total 17 marks)

a) Demonstrate understanding of: i) The nomenclature and corresponding displayed formulae for: alkanes, alkenes,

cycloalkanes and cycloalkenes ii) The following terms as associated with the structure of organic molecules: empirical

and molecular formulae; isomerism, structural isomers and geometric isomers (limited to cis-trans isomers about a double bond)

iii) The following terms as associated with organic reactions: homolytic and heterolytic fission; free radical, photochemical reaction; chain reaction, initiation, propagation, termination; electrophile; addition, substitution and elimination reactions; hydrolysis.

iv) Links to topic 2 b) Recall typical behaviour of the alkenes and alkanes, limited to:

• Combustion and cracking • Polymerisation of alkenes • Treatment with:

i. Acidified potassium permanganate (VII) ii. Halogens

iii. Concentrated sulphuric acid c) Interpret the reactions of alkanes and alkenes in terms of the processes of bond-breaking and

bond-making by electrophilic or free radical attack and by reference, as appropriate, to electron pair availability, bond polarisation and bond energy

d) Recall uses of hydrocarbons

2. A possible route for making chloroethene in the laboratory is as follows:

C H 2 4 2 4 2 2 3C H Cl C H ClStep 1 Step 2

ethene 1,2–dichloroethane chloroethene Suggest reagents and conditions for each step.

Step 1 ......................................................................……….................................................

……….....................………..................................................................................................

Step 2 .......................................................................................................................……….

…….….……......................................................................................................................... (4)

3. (i) Write a balanced equation for the formation of poly(chloroethene) from chloroethene.

…….….….................................................................................................................. (1)

(ii) Suggest appropriate conditions for the polymerization reaction.

…….….…..................................................................................................................

…….….….................................................................................................................. (2)

(iii) State the type of polymerization reaction involved in the formation of poly(chloroethene).

…….….….................................................................................................................. (1)

(iv) Suggest a use for poly(chloroethene), explaining why it is suitable.

…….….…..................................................................................................................

…….….…..................................................................................................................

…….….….................................................................................................................. (1)

(Total 15 marks)

4. (a) Propane, C3H8, is used as a feedstock for making ethene using a cracking process. The yield of ethene is about 42%.

(i) Write an equation for the cracking of propane to form ethene using displayed formulae.

(2)

(ii) Draw a labelled diagram of an ethene molecule, showing the electron density distribution in the σ and π bonds between the carbon atoms.

(2)

(b) The cracking of propane also produces propene.

C H (g) C H (g) + H (g)3 8 3 6 2

Calculate the standard enthalpy change for this reaction. Use the data, at 298 K.

∆H f [C3H8(g)] = –104.5 kJ mol–1

∆H f [C3H6(g)] = +20.2 kJ mol–1

Your answer should include a sign and units.

(2)

(c) Propene can be used to make a number of important chemical products. The processes involved can be summarized in the diagram:

Compound A

Reaction 2 Reaction 1

B C and

Poly(propene)

CH CH –– CHPropene

2

2

3

Brin the dark

2 2CH CH –– CH –– Cl

CH ––C––CH

H

OH

3 3

Propan–2–ol

(i) Give the displayed formula and name of compound A.

Name................................................................................................................. (2)

(ii) State the type of reaction occurring and the type of reagent used in the formation of compound A.

Type of reaction .................................................................................................

Type of reagent .................................................................................................. (2)

(iii) Give the formulae of compounds B and C.

B .......................................................................................................................

C ....................................................................................................................... (2)

(iv) Write a balanced equation for the formation of poly(propene) for propene in Reaction 1.

(2)

(v) Suggest a reagent and condition for Reaction 2.

Reagent .............................................................................................................

Condition .......................................................................................................... (2)

(vi) State the type of mechanism in the substitution in Reaction 2.

.......................................................................................................................... (1)

(vii) Give the systematic name for CH2==CHCH2C1.

.......................................................................................................................... (1)

(Total 18 marks)

5. Butane reacts with chlorine, in a free radical chain reaction, to form 1–chlorobutane as one of the

products. The reaction takes place in a number of steps:

Step 1 Cl––Cl Cl + Cl

Step 2 Cl + CH CH CH CH CH CH CH CH + HCl

Step 3 CH CH CH CH + Cl CH CH CH CH Cl + Cl

Step 4 CH CH CH CH + Cl CH CH CH CH Cl

3

3

3 3

3

332

2

2 2

2

22

22

2 2

2

2

2

2 2

2

2

Initiation

Termination

(i) What condition is needed to promote Step 1?

.......................................................................................................................... (1)

(ii) What type of bond breaking occurs in Step 1?

.......................................................................................................................... (1)

(iii) Classify the type of reaction step occurring in Steps 2 and 3.

.......................................................................................................................... (1)

(iv) Suggest an equation for another possible chain termination step.

(1)

(v) Give one other example of a reaction with a free radical chain mechanism.

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (1)

(Total 5 marks)

6. Steam distillation is often used to obtain chemicals such as lavender oil and limonene from plants.

(a) (i) Explain why heating the plants directly, to distil off their oil, is not usually successful.

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..……………………………………………………………. (2)

(ii) How does steam distillation overcome these problems?

…………………..…………………………………………………………….

…………………..……………………………………………………………. (1)

(b) (i) Draw a labelled diagram of a suitable apparatus for steam distillation to obtain an oil from lemon peel.

(3)

(ii) How would you obtain a pure, dry sample of the oil from the mixture obtained by steam distillation?

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..……………………………………………………………. (2)

(c) (i) The oil obtained turns dilute acidified potassium manganate(VII) from pink to colourless. Which functional group does this suggest is present in the oil?

…………………..…………………………………………………………….

…………………..…………………………………………………………….

…………………..……………………………………………………………. (1)

(ii) The dry oil reacts with sodium to give off hydrogen. Which functional group does this suggest is present in the oil?

…………………..…………………………………………………………….

…………………..……………………………………………………………. (1)

(Total 10 marks)

7. Cracking is an important process in the petrochemical industry. Cracking the fraction of crude oil with a boiling range of 200–300 °C produces a number of useful alkanes and alkenes.

(a) Why does the original fraction of crude oil have a boiling range rather than a single boiling point?

.....................................................................................................................................

..................................................................................................................................... (1)

(b) The following equation represents one possible reaction which might occur during cracking.

(i) Give the name of Product 1.

............................................................................................................................ (1)

(ii) Give the molecular formula of Product 1.

............................................................................................................................ (1)

(iii) Product 1 of this reaction is used as a component of petrol. Suggest ONE reason why it is more suitable for this use than the original undecane.

............................................................................................................................

............................................................................................................................ (1)

(iv) State TWO necessary conditions used when cracking petroleum fractions.

............................................................................................................................

............................................................................................................................ (2)

(v) Draw a labelled diagram showing suitable apparatus and materials for ‘cracking’ a liquid such as ‘light paraffin’ in the laboratory. You should indicate how a gaseous product of the reaction could be collected.

(4)

(c) There are several isomers of Product 2. One of them, an alkene, can be made from 2-bromo-2-methylpropane, which has the following formula:

(i) Draw the structural formula of the alkene produced.

(1)

(ii) Name the type of reaction involved in the conversion of 2-bromo-2-methylpropane to Product 2.

............................................................................................................................ (1)

(iii) What reagent and conditions would be used to bring about this conversion?

Reagent ..............................................................................................................

Conditions .......................................................................................................... (2)

(Total 14 marks)

8. This question is concerned with alkenes including ethene and buta-1,3-diene, CH2 = CHCH = CH2.

(a) (i) The typical reactions of alkenes are addition reactions, for example their reactions with bromine.

Explain why the reaction of ethene with bromine is described as an addition reaction.

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (1)

(ii) Why should this reaction be carried out in the absence of sunlight or ultra-violet radiation?

..........................................................................................................................

.......................................................................................................................... (1)

(iii) Explain how, in this reaction, the bromine molecule is able to act as an electrophile, even though it is normally non-polar.

(2)

(b) (i) When 1 mole of bromine molecules is added to 1 mole of buta-1,3-diene, the principal product is 1,4-dibromobut-2-ene, CH2BrCH = CHCH2Br, a compound which exists as two geometric isomers.

Draw the displayed formulae of both of these two isomers.

(2)

(ii) State why geometric isomerism is possible in 1,4-dibromobut-2-ene. [You may find it helpful to refer to the formulae you have drawn above].

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (1)

(c) It has been suggested that cyclohexene, another alkene, could be made by a reaction between ethene and buta-1,3-diene.

Using molecular formulae, the reaction could be represented by the equation

C2H4(g) + C4H6(g) C6H10(l) ∆H = –200 kJ mol–1

(i) Draw the displayed formula of cyclohexene.

(1)

(ii) Decide whether high or low temperature and pressure would give the higher proportion of cyclohexene at equilibrium. Justify your choice in each case.

Temperature .....................................................................................................

..........................................................................................................................

Pressure ............................................................................................................

..........................................................................................................................

.......................................................................................................................... (2)

(Total 10 marks)

10. The reaction between chlorine and methane, in the presence of ultraviolet light, involves the formation

of free radicals and includes the following steps:

A Cl2 → 2Cl• ∆Ηο = +242 kJ mol–1

B CH4 + Cl• → HCl + CH3• ∆Η

ο = +4 kJ mol–1

C Cl2 + CH3• → CH3Cl + Cl• ∆Η

ο = –97 kJ mol–1

D Cl• + Cl• → Cl2

E CH3• + CH3

• → CH3CH3

F Cl• + CH3• → CH3Cl ∆Η

ο = –339 kJ mol–1

(a) (i) What is meant by a free radical? ....................................................................

...........................................................................................................................

........................................................................................................................... (1)

(ii) Draw a ‘dot-and-cross’ diagram, showing outer shell electrons only, for a chlorine free radical.

(1)

(iii) What type of bond breaking occurs in step A?

........................................................................................................................... (1)

(b) Which of the steps, A to F, are chain propagation steps?

........................................................................................................................... (1)

(c) (i) Write the equation for the overall reaction between one mole of chlorine and one mole of methane molecules.

(1)

(ii) Calculate the standard enthalpy change, ∆Η

ο, for this reaction.

(2)

(d) (i) What is the value of ∆Ηο for step D? ................................................................ (1)

(ii) Would you expect step E to be exothermic or endothermic? Justify your answer.

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (1)

(e) The overall reaction was repeated using bromine gas instead of chlorine gas.

Would you expect step A for bromine to be more or less endothermic than step A for chlorine? Justify your answer.

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (2)

(Total 11 marks)

a) Demonstrate understanding of the nomenclature and corresponding displayed and structural

formulae for halogenoalkanes b) Recall the typical behaviour of halogenoalaknes, limited to:

i) Combustion ii) Treatment with:

• Aqueous alkali • Alcoholic alkali • Aqueous silver nitrate • Alcoholic ammonia

c) Interpret the reactions of halogenoalkanes in terms of the processes of bond-breaking and bond-making by nucleophilic attack and by reference, as appropriate, to electron pair availability, bond polarisation and bond energy

d) Recall the uses of halogenoalkanes e) Demonstrate understding of the following terms as associated with organic rections;

homolytic and heterolytic fission; free radical, photochemical reaction; chain reaction, initiation, propagation, termination; electrophile; addition, substitution and elimination reactions; hydrolysis

1. Chloroethene, C2H3C1, is the monomer from which the important plastic poly(chloroethene) is made. It is often known as PVC. It can be produced with any degree of flexibility from rigid to pliable.

(i) Draw the displayed formula of chloroethene.

(1)

(ii) Draw a ‘dot–and–cross’ diagram of a chloroethene molecule. You need include only outer shell electrons.

(2)

2. A possible route for making chloroethene in the laboratory is as follows:

C H 2 4 2 4 2 2 3C H Cl C H ClStep 1 Step 2

ethene 1,2–dichloroethane chloroethene

Suggest reagents and conditions for each step.

Step 1 ......................................................................……….................................................

……….....................………..................................................................................................

Step 2 .......................................................................................................................……….

…….….……......................................................................................................................... (4)

3. (a) This part of the question is about the hydrolysis of halogenoalkanes.

2 cm3 of ethanol is added to each of three test-tubes.

Three drops of 1–chlorobutane are added to the first, three drops of 1–bromobutane to the second, and three drops of 1–iodobutane to the third test-tube.

2cm3 portions of hot aqueous silver nitrate solution are added to each test-tube.

A precipitate forms immediately in the third test-tube, slowly in the second test-tube and extremely slowly in the first test-tube.

In each reaction the precipitate is formed by silver ions. Ag+(aq), reacting with the halide ions formed by hydrolysis of the halogenoalkane.

(i) Why was ethanol added to each test-tube?

..........................................................................................................................

(1)

(ii) The same organic product forms in each reaction.

Name this organic product.

.......................................................................................................................... (1)

(iii) Complete the equation for the hydrolysis of 1–bromobutane

C4 H9 Br + H2O → (2)

(iv) What is the colour of the precipitate in the third test-tube?

.......................................................................................................................... (1)

(v) Name the precipitate which forms extremely slowly in the first test-tube and write the ionic equation, including state symbols, for its formation.

Name of precipitate............................................................................................

Ionic equation.................................................................................................... (3)

(vi) Ammonia solution is added to the precipitate formed in the first test-tube. Describe and explain what you would observe.

Description........................................................................................................

..........................................................................................................................

Explanation........................................................................................................

.......................................................................................................................... (2)

(vii) Explain why the rates of hydrolysis of the three halogenoalkanes are different

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (2)

(b) 1–bromobutane reacts with an alcoholic solution of potassium hydroxide at high temperature to form but–1–ene.

(i) Draw a fully labelled diagram to show an apparatus for carrying out this reaction in the laboratory and collecting the gaseous but–1–ene

(3)

(ii) Suggest a chemical test for an alkene such as but–1–ene. State the colour change you would observe.

Reagent.............................................................................................................

Colour change from.................................................to....................................... (2)

(Total 17 marks)

4. (a) This part of the question is about the hydrolysis of halogenoalkanes.

2 cm3 of ethanol is added to each of three test-tubes.

Three drops of 1–chlorobutane are added to the first, three drops of 1–bromobutane to the second, and three drops of 1–iodobutane to the third test-tube.

2cm3 portions of hot aqueous silver nitrate solution are added to each test-tube.

A precipitate forms immediately in the third test-tube, slowly in the second test-tube and extremely slowly in the first test-tube.

In each reaction the precipitate is formed by silver ions, Ag+(aq), reacting with the halide ions formed by hydrolysis of the halogenoalkane.

(i) Why was ethanol added to each test-tube?

.......................................................................................................................... (1)

(ii) The same organic product forms in each reaction.

Name this organic product.

.......................................................................................................................... (1)

(iii) Complete the equation for the hydrolysis of 1–bromobutane.

C4H9Br + H2O → (2)

(iv) What is the colour of the precipitate in the third test-tube?

.......................................................................................................................... (1)

(v) Name the precipitate which forms extremely slowly in the first test-tube and write the ionic equation, including state symbols, for its formation.

Name of precipitate ...........................................................................................

Ionic equation .................................................................................................... (3)

(vi) Ammonia solution is added to the precipitate formed in the first test-tube. Describe and explain what you would observe.

Description ......................................................................................................

..........................................................................................................................

Explanation ..................…................................................................................

.......................................................................................................................... (2)

(vii) Explain why the rates of hydrolysis of the three halogenoalkanes are different.

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (2)

(b) 1–bromobutane reacts with an alcoholic solution of potassium hydroxide at high temperature to form but–1–ene.

(i) Draw a fully labelled diagram to show an apparatus for carrying out this reaction in the laboratory and collecting the gaseous but–1–ene.

(3)

(ii) Suggest a chemical test for an alkene such as but–1–ene. State the colour change you would observe.

Reagent ............................................................................................................

Colour change from ......................................... to …....................................... (2)

(Total 17 marks)

5. This question is about some of the reactions of the halogens.

(a) Chlorine solution, Cl2 (aq), is added to potassium bromide solution and potassium iodide solution in separate test–tubes.

To help identify the products an equal volume of hydrocarbon solvent is shaken with the contents of each test–tube.

(i) State the colour of the hydrocarbon solvent at the end of each reaction with chlorine.

Potassium bromide reaction ………………………………………………….

Potassium iodide reaction ……………………………………………………. (2)

(ii) Why does only one product from each reaction dissolve in the hydrocarbon solvent?

…………………..…………………………………………………………….

…………………..……………………………………………………………. (1)

(iii) Write the equation, including state symbols, for the reaction between chlorine solution and potassium bromide solution.

(2)

(b) Bromine solution reacts with alkanes such as methane, and alkenes such as ethene.

(i) State the condition needed to promote the reaction between methane and bromine.

…………………..……………………………………………………………. (1)

(ii) Name the type and mechanism of the reaction between methane and bromine.

Type …………………………………………………………………………..

Mechanism …………………………………………………………………… (2)

(iii) Name the product of the reaction between ethene and bromine and draw a ‘dot–and–cross’ diagram of the structure for this product, showing outer electrons only.

Name …………………………………………………………………………. (2)

(c) Concentrations of oxidizing agents which will oxidize iodide ions to iodine can be measured by titrating the resulting iodine with a standard sodium thiosulphate solution.

10.0 cm3 samples of a solution containing 0.0100 mol dm–3 of iodine, I2, were found to react

with exactly 20.0 cm3 of a 0.0100 mol dm–3 aqueous solution of sodium thiosulphate.

Calculate the number of moles of iodine and sodium thiosulphate that react together and write the equation for the reaction between iodine and sodium thiosulphate.

Show how your equation is consistent with your calculation. (3)

(d) (i) What is the biological action that is common to all three solutions of chlorine, bromine, and iodine?

…………………..……………………………………………………………. (1)

(ii) Give ONE everyday application of one of these solutions acting in this way. (1)

(Total 15 marks) 6. One of the most important industrial uses of chlorine is in the production of poly(chloroethene),

usually called PVC. A sequence of reactions used to make PVC is set out below.

(a) (i) Name compound A.

.......................................................................................................................... (1)

(ii) Give the structural formula of chloroethene.

(1)

(iii) It is important that hydrogen chloride gas is not allowed to escape into the atmosphere.

Suggest a way in which its escape could be prevented.

..........................................................................................................................

.......................................................................................................................... (1)

(b) (i) Chloroethene is polymerised by a reaction involving free radicals. Explain what is meant by a free radical.

..........................................................................................................................

.......................................................................................................................... (1)

(ii) Give a necessary condition for the production of free radicals.

..........................................................................................................................

.......................................................................................................................... (1)

(c) (i) Ethane-1,2-diol, CH2OHCH2OH, is a useful compound which could be made from

compound A using a nucleophilic substitution reaction.

Suggest a suitable nucleophile for this reaction.

.......................................................................................................................... (1)

(ii) The diagram below shows part of the formula of compound A. Use the diagram to show how your suggested nucleophile attacks A.

C Cl

(2)

(iii) What is the leaving group in this reaction?

.......................................................................................................................... (1)

(iv) Suggest a suitable chemical test you could use to confirm the identity of this leaving group.

You should state the reagent you would use and give the observation expected.

..........................................................................................................................

.......................................................................................................................... (2)

(Total 11 marks)

7. The flow chart below shows some of the reactions of alcohols, alkanes, alkenes and halogenoalkanes.

(a) Compound A, C4H9Cl, is a tertiary halogenoalkane.

Draw the displayed formula for A and state its name.

Displayed formula

Name .......................................................................................................................... (2)

(b) The halogenoalkane A can be formed from the alcohol D.

(i) What reagent could be used to bring about this reaction? ...............................

.......................................................................................................................... (1)

(ii) State the type and mechanism of this reaction.

Type ................................................................................................................

Mechanism ...................................................................................................... (2)

(c) When Ais heated with concentrated, alcoholic potassium hydroxide, only one alkene, B, can be formed.

(i) Draw the displayed formula for B and state its name.

Displayed formula

Name ................................................................................................................ (2)

(ii) Can B exist as geometric isomers? Explain your answer.

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (1)

(d) State the type of reaction in the conversion of

B to C .........................................................................................................................

B to E .......................................................................................................................... (2)

(e) Draw the displayed formula for E.

(1)

(Total 11 marks)

8. The industrial processes involved in the production of poly(chloroethene) are summarised in the flow chart:

ethane → ethene → 1,2-dichloroethane → chloroethene → poly(chloroethene)

(a) (i) Ethane is converted to ethene by dehydrogenation.

Write a balanced equation, including state symbols, for this equilibrium reaction.

(1)

(ii) Explain why conditions of high pressure are less favourable for ethene production.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................ (2)

(b) Draw a labelled diagram of an ethene molecule, showing the electron density distribution in the σ and π bonds between the carbon atoms.

(2)

c) Give a chemical test which would distinguish between ethane and ethene.

State the result of your test with ethene.

Test ..............................................................................................................................

Result ........................................................................................................................... (2)

(d) 1,2-dichloroethane is formed from ethene by reaction with chlorine.

State the type and mechanism of this reaction.

Type ...................................................................................................................................

Mechanism ......................................................................................................................... (2)

(e) (i) Suggest a reagent and TWO conditions for making chloroethene from 1,2-dichloroethane in the laboratory.

Reagent .......................................................................................................................

Conditions ................................................................................................................... (2)

(ii) Name both types of intermolecular force between chloroethene molecules.

.............................................................................................................................

............................................................................................................................. (1)

(f) (i) Write a balanced equation for the formation of poly(chloroethene) from chloroethene.

(2)

(ii) Poly(chloroethene) is also known by the name polyvinylchloride, PVC.

Give TWO common uses of poly(chloroethene).

.............................................................................................................................

............................................................................................................................. (2)

(Total 16 marks) 9. Some reactions of 2-bromobutane are shown in the scheme below:

(a) (i) Name the reagent R and give the conditions under which Reaction 1 takes place.

Name of reagent R ...........................................................................................

Conditions ........................................................................................................ (2)

(ii) Give the type and mechanism of Reaction 1.

Type .................................................................................................................

Mechanism ...................................................................................................... (2)

(b) (i) Give the structural formula of the organic compound S formed in Reaction 2.

(1)

(ii) A precipitate would also be formed during this reaction. State its colour. Write an ionic equation, with state symbols, for its formation. Omit any spectator ions.

Colour of precipitate ..............................................................................................

Ionic equation

(2)

(iii) A similar experiment was carried out with 2-chlorobutane, rather than 2-bromobutane.

What difference would there be in the rate of formation of a precipitate?

Explain your answer.

...............................................................................................................................

...............................................................................................................................

............................................................................................................................... (2)

(c) (i) In Reaction 3, give the name of a suitable reagent T and describe the reaction conditions used.

Name of reagent T .................................................................................................

Conditions .............................................................................................................. (2)

(ii) Draw displayed formulae of the two geometric isomers of CH3CH==CHCH3.

(1)

(iii) Explain why CH2==CHCH2CH3 does not possess geometric isomers.

....................................................................................................................

...............................................................................................................................

............................................................................................................................... (1)

(Total 13 marks) 10. (a) The table below gives the boiling points of three organic compounds.

Compound Boiling point /K

chloroethane 285

1-chloropropane 320

2-chloropropane 309

(i) Explain why 1-chloropropane has a higher boiling point than chloroethane.

................................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................ (2)

(ii) Explain why 1-chloropropane has a higher boiling point than its isomer, 2-chloropropane.

................................................................................................................................

................................................................................................................................

................................................................................................................................ (1)

(b) Both chloroethane and iodoethane react with aqueous potassium hydroxide solution to form ethanol. The hydroxide ions act as nucleophiles.

(i) What is a nucleophile?

................................................................................................................................

................................................................................................................................

................................................................................................................................ (1)

(ii) Explain why iodoethane reacts faster than chloroethane with aqueous potassium hydroxide, under the same conditions.

................................................................................................................................

................................................................................................................................ (1)

(c) (i) Under what conditions does chloroethane react with potassium hydroxide to form ethene rather than ethanol?

...............................................................................................................................

............................................................................................................................... (1)

(ii) Name the type of reaction in which ethene is formed from chloroethane.

............................................................................................................................... (1)

(d) Ethanol can be produced from ethene in two stages. In the first stage ethene is reacted with concentrated sulphuric acid in an addition reaction.

(i) Complete the equation to show the product of the first stage in the process.

(1)

(ii) What type of addition reaction is occurring?

............................................................................................................................... (1)

(iii) How is the product of this reaction converted to ethanol?

............................................................................................................................... (1)

(e) In industry, ethanol is usually manufactured from ethene, rather than by reacting chloroethane with aqueous potassium hydroxide. Suggest a reason for this.

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

(1)

(Total 11 marks)